what is effervescent granules? How to prepare it?

Answer 1

You take a portion of citric acid, grind that together with sodium bicarbonate, seal the mixture in water-tight, air-tight packets and wait to use. Next, you take a small glass bottle with a rubber-stoppered glass seal, held by a thick wire retainer. You take ice-water, pour it in the bottle, dump in the effervescent powder, seal the bottle with the thick wire retainer, and wait. The mixture fizzes. The mixture calms down. You unseal the bottle, pour carefully into a glass, and enjoy lemon soda.

You might also read "The Mysterious Flame of Queen Loanna," a novel by Umberto Eco. In it, the protagonist describes discovering a box of these packets, 100 years old, in an old house, together with directions about how to use them.